the fact that there are miles and
miles of snow-fields, thousands of feet deep, on the mountain-tops and
in the gorges, to which fresh snows are added every winter, so that the
weight of what is behind, slipping off the slopes and falling from the
cliffs, crushes down and forward that which is below; thus glaciers
cannot choose but advance."

"Ay, ay," said the Captain, "no doubt no doubt that may be so; but why
is it that, bein' as brittle as glass, a glacier don't come rumblin' and
clatterin' down the valleys in small hard bits, like ten thousand
millions of smashed-up chandeliers?"

"Ay, there's the rub," exclaimed Lewis; "what say you to that?"

"Ha!" exclaimed the Professor, again smiling blandly, "there you have
touched what once was, and, to some philosophers it seems, still is, the
great difficulty. By some great men it has been held that glacier ice
is always in a partially soft, viscid, or semi-fluid condition, somewhat
like pitch, so that, although _apparently_ a solid, brittle, and rigid
body, it flows sluggishly in reality. Other philosophers have denied
this theory, insisting that the ice of glaciers is _not_ like pitch, but
like glass, and that it cannot be squeezed without being broken, nor
drawn without being cracked. These philosophers have discovered that
when ice is subjected to great pressure it melts, and that, when the
pressure is removed, the part so melted immediately freezes again--hence
the name regelation, or re-freezing, is given to the process. Thus a
glacier, they say, is in many places being continually melted and
continually and instantaneously re-frozen, so that it is made to pass
through narrow gorges, and to open out again when the enormous pressure
has been removed. But this theory of regelation, although
unquestionably true, and although it exercises _some_ influence on
glacier motion, does not, in my opinion, alone account for it. The
opinion which seems to be most in favour among learned men--and that
which I myself hold firmly--is, the theory of the Scottish Professor
Forbes, namely, that a glacier is a semi-fluid body, it is largely
impregnated throughout its extent with water, its particles move round
and past each other--in other words, it flows in precisely the same
manner as water, the only difference being that it is not quite so
fluid; it is sluggish in its flow, but it certainly models itself to the
ground over which it is forced by its own gravity, and it is onl